Studies have been done for economically viable processes to produce butanol. Like ethanol, butanol may be a possible solution to dependency on oil as both may be used as a fuel in an internal combustion engine. In fact, due to the longer hydrocarbon chain and non-polar characteristics, butanol may be a better fuel option than ethanol because butanol is more similar to gasoline than ethanol. In addition, butanol may be used in the manufacture of pharmaceuticals, polymers, pyroxylin plastics, herbicide esters and butyl xanthate. Butanol may also be used as a solvent for the extraction of essential oils or as an ingredient in perfumes; as an extractant in the manufacture of antibiotics, hormones, and vitamins; as a solvent for paints, coatings, natural resins, gums, synthetic resins, alkaloids, and camphor. Other applications of butanol includes as swelling agent in textiles; as a component of break fluids, cleaning formulations, degreasers, and repellents; and as a component of ore floatation agents and of wood-treating systems.
Butanol is typically produced industrially from petrochemical feedstock propylene in the presence of a rhodium-based homogeneous catalyst. During this process, propylene is hydroformylated to butyraldehyde and butyraldehyde is then hydrogenated to product butanol. However, due to the fluctuating natural gas and crude oil prices the cost of producing butanol using this method also becomes more unpredictable and significant.
It is known that butanol may be prepared by condensation from ethanol over basic catalyst at high temperature using the Guerbet reaction. The reaction mechanism for the conversion of ethanol to butanol via the Guerbet reaction comprises a four-step sequence as shown in reaction scheme 1. In the first step, ethanol is oxidized to intermediate aldehyde and two of the intermediate aldehydes undergo an aldol condensation reaction to form crotonaldehyde, which is reduced to butanol via hydrogenation. See, for example, J. Logsdon in Kirk-othmer Encyclopedia of Chemical Technology, John Wiley and Sons, Inc., New York, 2001; J. Mol. Catal. A: Chem., 2004, 212, p. 65; and J. Org. Chem., 2006, 71, p. 8306.

Various catalysts have been studied to improve the conversion and selectivity of ethanol to butanol. For example, M. N. Dvornikoff and M. W. Farrar, J. of Organic Chemistry (1957), 11, 540-542, discloses the use of a MgO—K2CO3—CuCrO2 catalyst system to promote ethanol condensation to higher alcohols, including butanol. U.S. Pat. No. 5,300,695 discloses processes where an L-type zeolite catalyst, such as a potassium L-type zeolite, is used to react with an alcohol having X carbon atoms to produce alcohol with higher molecular weight.
The use of hydroxyapatite Ca10(PO4)6(OH)2, tricalcium phosphate Ca3(PO4)2, calcium monohydrogen phosphate CaHPO4.(0-2)H2O, calcium diphosphate Ca2P2O7, octacalcium phosphate Ca8H2(PO4)6.5H2O, tetracalcium phosphate Ca4(PO4)2O, or amorphous calcium phosphate Ca3(PO4)2.nH2O, to convert ethanol to higher molecular weight alcohols are disclosed in WO2006059729.
Carlini et al., Journal of Molecular Catalysis A: Chemical (2005), 232, 13-20, discloses bifunctional heterogeneous hydrotalcites for converting methanol and n-propanol to isobutyl alcohol.
Others catalyst systems for making higher molecular weight alcohols from methanol or ethanol have also been studied. For example, U.S. Pat. No. 4,551,444 discusses the use of multi-component catalyst system using various metals; U.S. Pat. Nos. 5,095,156 and 5,159,125 discuss the impact of magnesium oxide; U.S. Pat. No. 4,011,273 discusses the use of insoluble lead catalysts; U.S. Pat. No. 7,807,857 focuses on Group II metal salts; and U.S. Pat. No. 4,533,775 discusses a catalyst system comprising a metal acetylide, a hydride, an alkoxide and promoter.
The references mentioned above are hereby incorporated by reference.
Nonetheless, the need remains for improved catalysts for making butanol from ethanol, especially those having improved activity and selectivity to butanol.